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Abstract:

The presence of toxic metals and organic substances in environmental waters has serious implications for human health. The extraction and pre-concentration of these substances from 'ater samples is a core component of their determination. 'Ibis thesis introduces newly developed nanoscavengers for the extraction and pre-concentration.of harmful substances - om water samples~ using a new s,olid phase dispersion extraction technique (SPDE). This technique is based on the dispersion of 250 nm diameter, mqdified silica particles (nanoscavengers) in water samples, to extract the analytes. Uniform silica particles were synthesised by both a conventional sol-gel process and a new spray technique. The parameters influencing their formation were investigated, and it was found that the concentration of tetraethoxysilane (TEOS), ammonia, solvent, temperature and agitation, can all affect the final particle size. The silica particles were characterized by scanning electron microscopy (SEM) and particle size analysis. Under optimal conditions, very uniform and monodisperse silica spherical particles, having the target diameter of 250 nm 8 nm), were obtained. Different types of nanoscavenger were synthesised by modification of the silica with a number of silane coupling agents, such as N-[3-(trimethoxysilyl)propyl]-ethylenediamine and its dithiocarbamate, 3-mercaptopropyltrimethoxysilane, octadecyltrichlorosilane and octadecyltrimethoxysilane. The modification step was carried out by two different processes: the modification of pre-formed 250 nm silica particles and by a single-pot synthesis. Both processes showed a successful immobilization of silylating agents with a variation of loading. The amino-nanoscavenger, when applied to the pre-concentration of copper from water gave a recovery of 98%. A dithiocarbamate-nanoscavenger was applied to the preconcentration of cadmium, copper~ lead and nickel and recoveries were 99, 97, and 92%, respectively. Inorganic mercury and arsenic were pre-concentrated using a mercaptonanoscavenger, and recoveries of 106 and 96% were obtained, respectively. The collection of organic species using the C1S-nanoscavenger resulted in the recovery of 70% di-n-butyl phthalate. Herbicides such as Atrazine, Ramrod, Diuran and Propazine were recovered efficiencies of 66, 78, 82 and 59%, respectively. A dual-functionalitynanoscavenger was employed for the pre-concentration of 22 chlorinated pesticides, and recoveries varied from 70 to 100%. Polynuclear aromatic hydrocarbons (PAHs) were also pre-eoncentrated from water samples using this dual-functionality-nanoscavenger, and recoveries of 13 PARs varied from 70 to Nanoscavenger based solid phase dispersion extraction 'SPDE' offers many advantages over conventional approaches. These include the minimization of regents, transportability, field application and efficiency.